This invention relates to a method and apparatus for cellular communication. More particularly, this invention relates to a method and apparatus for setting up a call between at least one standard analog terminal and a remote terminal in a network, via a radio terminal, or accessing a remote terminal or requesting a special service in a network from at least one standard analog terminal, via a radio terminal, while the radio terminal is engaged in a conversation with another remote terminal in the network.
Cellular radio telephone systems provide for communication among mobile stations and fixed telephone networks. Typically, a cellular system includes cellular transceivers or terminals connected to a Radio Base Station (RBS) that enables calls to be transmitted to and received from the cellular network via a Base Station Controller (BSC) and a Mobile Switching Center (MSC).
A standard Plain Old Telephone System (POTS) telephone can be interfaced with a fixed cellular terminal (FCT) so that a call can be set up at or received by the POTS telephone terminal via the FCT, avoiding the need for wiring the POTS telephone to a local exchange. The FCT alerts the POTS telephone when an incoming call is received, causing the POTS telephone to ring. The FCT is typically implemented with a modified cellular radio terminal that provides the line card functions normally provided by the local exchange in the POTS.
A difficulty that arises in interfacing standard POTS telephones with FCTs is that the procedure by which a telephone connection is established in a POTS is different from the procedure by which a connection is established in a cellular radio telephone system.
In a POTS, the line card in the local exchange provides a dial tone when the POTS telephone goes off-hook. After the first dialed digit is received in the line card from the POTS telephone, the dial tone is terminated, and the line card continues to receive subsequently dialed digits in sequence, passing them directly to the group switch. The group switch analyzes the dialed digits and makes a connection to the telephone terminal corresponding to the dialed digits, if the sequence of dialed digits is valid. If a complete or valid dialing sequence is not received by the group switch before a timer has expired, the group switch releases the connection, and the line card sends a busy signal or an error signal to the POTS telephone.
In contrast, in a cellular radio telephone system, a subscriber uses the keypad of a cellular terminal, such as a mobile telephone, to enter dialed digits into a memory and then presses a dedicated `SEND` key which initiates call set up processing. In the cellular terminal, call set up processing generally begins by scanning for control channels broadcast by the RBS, locking onto one of the available control channels, and receiving and decoding overhead information. The cellular terminal then transmits a random access message to the RBS requesting call set up. The request usually involves some type of authentication handshake between the RBS and the cellular terminal. After authentication and further communication, a voice channel is eventually opened, and the call is completed. The details of call set up processing vary depending upon the air interface standard (e.g., AMPS, TACS, GSM, IS-136, IS-95, etc.) employed by a particular cellular system.
A problem encountered when interfacing a POTS telephone with an FCT is that a POTS telephone does not have a `SEND` key. Thus, some other way must be provided for a POTS telephone to initiate the call set up processing in the FCT.
Several systems have been proposed for overcoming this problem of interfacing a standard POTS telephone with an FCT. For example, U.S. Pat. No. 4,718,080 to Serrano discloses a system in which, after a telephone number is dialed at a standard POTS telephone, a `SEND` signal is simulated, and the dialed digits are transmitted to the cellular terminal. Dialing sequences can also be entered at the standard POTS telephone to control features of the standard POTS telephone, such as volume control. U.S. Pat. No. 4,658,096 to West, Jr. et al. and its related patents disclose a system in which a `SEND` signal is transmitted to a cellular terminal after the last digit has been dialed at the standard POTS telephone. The system determines whether the last digit has been dialed based on a logical analysis of the dialed digits or on time elapsed after the last digit has been dialed. A problem with these approaches is that some sort of determining algorithm or a timer is required to determine when the last digit is dialed, which increases the cost and complexity of the FCT.
Systems employing predetermined dialing sequences to instruct a cellular terminal to perform certain functions are also known. For example, U.S. Pat. No. 4,959,851 to Tobolski, Jr. et al. discloses a system in which predetermined dialing sequences consisting of leading and trailing function digits are entered at a standard POTS telephone to select features of a cellular terminal. Other systems employ an End Of Number (EON) key method, in which the user explicitly decides when to send dialed digits to the cellular terminal by pressing a predetermined key. For example, U.S. Pat. No. 5,117,450 to Joglekar et al. discusses pressing "#" or "*" to send dialed digits to a cellular transceiver. A drawback of such systems is that they require the user to press a particular function key or key sequence, which can be cumbersome and easily forgotten.
Another proposed solution is a Digit by Digit method, in which a certain number of roamer ports are assigned in the MSC for the FCT subscribers. When a POTS telephone goes off hook, a call to one of the roamer ports in the MSC is automatically performed via an FCT. When a voice or traffic channel is assigned to the calling FCT, the MSC generates a dial tone that is sent to the FCT through the voice or traffic channel. The user then initiates dialing, and the dialed digits are sent as dual tone multi-frequency (DTMF) tones through the voice or traffic channel to the MSC. These dialed digits are stored in the roamer port, forming the complete called number. A problem with this approach is that it requires a change in the configuration of existing MSCs or the installation of new MSCs, which can be prohibitively expensive.
Thus, it is an objective of the present invention to provide an improved method and apparatus for setting up a call between at least one standard analog terminal and a remote terminal in a network, via a radio terminal, which overcomes the drawbacks mentioned above. It is also an objective of the present invention to provide an improved method and apparatus for accessing a remote terminal or requesting a service in a network from at least one standard analog terminal via a radio terminal, while the radio terminal is engaged in a conversation with another remote terminal in the network, which overcomes the drawbacks mentioned above.